1. Field
This invention relates to using siliceous glassy, low-density macroporous materials as biosupports for bacteria.
2. Description of Previously Published Art
Catalytic biosupports are hosts for bacteria which metabolize toxic or polluting chemicals in waste streams into environmentally harmless products. This is usually done by pumping the liquid through a reactor vessel containing the bacteria on an inorganic host media. Properties of the support for this application include:
attraction of the bacteria to the support material, PA1 high surface area, PA1 mechanical integrity, PA1 non-biocidal, PA1 cost effective, PA1 insensitive to process upsets (e.g. pH, temperature, concentration of organic waste, etc.), and PA1 large macropore volume to sustain bacterial growth and diffusion of nutrients.
Examples of currently used materials are granulated carbon; extruded diatomaceous earth, clay, and zeolites; plastics; biofilms; and various extruded ceramic oxides. The majority of existing products contain primarily micropores (&lt;1000 .ANG.) or limited macroporosity at or near the surface of the media. This limits the surface area on the media which is an effective host for microorganisms. Furthermore, most manufactured media require extensive powder processing and fabrication methods which may include mixing and milling of raw materials, spray drying, formulation development, forming (extrusion, injection molding, etc.), cutting, drying and calcining. The final cost of the product necessarily reflects the cost of raw materials, processing and fabrication.
Processes such as extrusion generally impose a compromise between strength and porosity, two critical properties which conflict with one another in most commercial processes. Highly macroporous materials generally mean low strengths, and vice-versa. Desired sizes of macropores for bioremediation are at least 1000 .ANG., and preferentially 10,000 .ANG.. Pore volume ranges from 0.1 to about 0.5 cc/cc for biosupports. Increases in macropore volume and surface area mean greater area on which the bacteria can live. Greater concentrations of bacteria, in turn, metabolize larger amounts of waste organics into environmentally safe products.
Mechanical durability is important against attrition in both fixed and moving bed reactors, as well as during handling and transportation. In fabricated ceramic articles made from, for example, diatomaceous earth or clay, low calcination (sintering) temperatures maintain high porosity while creating limited grain boundary bonding. In general, these low temperatures do not provide high strengths relative to materials produced at very high temperatures or from a molten state.
Natural materials have been utilized in the manufacture of biosupports. Typical examples include the use of thermally-treated smectite clays (Krause, M., New Glass, 1990, 5(2), 209-16); sepiolite (J02252669 and J02238880); and sintering a mixture of natural silica rock, clay, feldspar, sericite, and alumina sediment to produce a low-density component for wastewater treatment (J03172168). Other patents teach the fabrication of media from inorganic ceramic materials such as alumina (J03049678); magnetic glass (J03505163); and titanium oxide, zirconium oxide or silicon carbide (J03087183).
Menke and Rehm (Applied Microbiology Biotechnology, 1992, 37:655-661) described the use of an unspecified lava rock as a substitute for the propagation of Alcaligenes bacteria. No physical properties (e.g., porosity, density, composition) were specified for the lava material. The term "lava" is an all-encompassing term which denotes any rock created by solidification of a natural molten source. No aspects of composition, texture, grain size, or physical properties can be inferred from the term. Lava encompasses a wide range of rock types including granites, gabbros, basalts, scorias and rhyolites, each of which possess a specific set of physical properties, compositions and origins.
Foerster, H., et al in Fortschr. Mineral., Beih., 63(2), 1-24 discuss Eifel lava and show that it is mainly basaltic in nature. It has been mined for use as a filler for trickling bed filters in sewage treatment applications. While other volcanic rocks are mined in this area, no others (including pumice) are mentioned as having use in waste treatment applications.
3. Objects of the Invention
It is an object of this invention to use macroporous low-density glassy materials as biosupports for the sustenance and propagation of bacteria for bioremediation wastewater treatment.
It is a further object of this invention to utilize biosupports from low cost, natural, commercially-available raw materials at a cost of less than 50 cents/pound.
It is a further object of this invention to utilize biosupports from selected naturally occurring siliceous materials having macroporosity and continuous pore structures which allow diffusion of nutrients throughout the body and hence bioactivity throughout media rather than strictly at or near the surface.
It is a further object of this invention to utilize biosupports having strength/abrasion resistance.
It is a further object of this invention to utilize biosupports for wastewater treatment with a low bulk density (0.8-1.2 g/cc).
It is a further object of this invention to utilize biosupports composed predominately of SiO.sub.2 (.ANG. 60 wt %).
It is a further object of this invention to utilize pumice mixed with at least one additional biosupport having unique properties (e.g., adsorption capabilities, buffering capacity, etc.) to produce a lower cost biosupport with tailorable properties.
These and further objects will become apparent as the description of the invention proceeds.